Possible to replace phone app?

Hi all,

I'm currently running VM12 by Team Nocturnal on my Galaxy S5. I've noticed that my phone app runs a little slow when picking up but most importantly, the mute button doesn't work.

I've searched around on the app store for phone app replacements but i have only found dialer apps and apps that make free calls. Is it possible for me to actually replace the phone app itself that uses my normal signal to make calls (not the dialer)?